This invention relates to a limiter circuit for alternating voltages, the circuit comprising a series arrangement of two diode groups, the groups being arranged in opposite sense and each group comprising at least one zener diode.
Such a circuit is known from for example U.S. Pat. No. 4,700,130 and serves for limiting an applied alternating voltage to a fixed value to protect subsequent circuit sections and circuit elements against excessive voltages. In the known circuit this is effected in that, depending on the polarity of the alternating voltage, the zener voltage of one of the zener diodes is exceeded if the instantaneous value of the alternating voltage exceeds the sum of the zener voltage of one of the diodes and the forward voltage of the second diode. In this way the limiter circuit restricts the alternating voltage to this value, the limiter voltage.
In many cases it is desirable to have a signal current which indicates that a limiter current flows in the limiter circuit, i.e. that the applied alternating voltage is limited to the limiter voltage. By means of this signal current it is possible, for example, to bring into effect further protective measures for the circuit sections following the limiter circuit. This signal current should always flow in the same direction and should suitably not be formed directly by the limiter current, which may assume large values under certain conditions.